This is a Processing Tutorial about:
How to save audio data to text files...
... and load this text file, prepare and display it.
This way you are able to visualize music, but your sketch doesn't have to run in realtime (e. g. complex visualizations, render your visualization). Most (or every?) Processing library doesn't support that.
Sorry for the bad and slow typing (misspellings, senseless word order). It's really tough for me to phrase, to type and think and the same time.
CocoRosie - The moon asked the crow